import pygame

class Ship():
	
	def __init__(self, ai_settings, screen):
		"""初始化飞船并设置其初始位置"""
		self.screen = screen
		self.ai_settings = ai_settings
		
		# 加载飞船图像并获取其外接矩形
		# 使用get_rect()获取相应surface的属性rect
		self.image = pygame.image.load('ship.bmp')
		self.rect = self.image.get_rect()
		self.screen_rect = screen.get_rect()
		
		# 将每艘新飞船放在屏幕底部中央
		self.rect.centerx = self.screen_rect.centerx
		self.rect.bottom = self.screen_rect.bottom
		
		# 在飞船的属性center中存储小数值
		self.center = float(self.rect.centerx)
		
		# 移动标志
		self.moving_right = False
		self.moving_left = False
				
	
	def update(self):
		"""根据移动标志更新飞船的位置 && 限制飞船的活动范围"""
		if self.moving_right and self.rect.right < self.screen_rect.right:
			self.center += (self.ai_settings.ship_speed_factor *
				self.ai_settings.time_passed)
		if self.moving_left and self.rect.left > 0:
			self.center -= (self.ai_settings.ship_speed_factor *
				self.ai_settings.time_passed)
		
		self.rect.centerx = self.center
			
	def blitme(self):
		"""在指定位置绘制飞船"""
		self.screen.blit(self.image, self.rect)

	def center_ship(self):
		"""让飞船恢复初始居中位置"""
		self.rect.centerx = self.screen_rect.centerx
